The present invention relates generally to water pollution traps and, more particularly, to oil/grit separators for separating and collecting various pollutants from storm-water runoff.
During rainstorms, water that is not absorbed into the ground runs off into storm sewer systems for delivery into freshwater systems such as streams, rivers, lakes, and wetlands. While flowing across parking lots, landscaped areas, and other surfaces, the storm-water runoff picks up debris and pollutants and carries them into the storm sewer systems. Particularly large amounts of pollutants are picked up at shopping centers with large parking lots, oil-change and auto-repair shops, gas stations, and so forth. These pollutants include motor oil and other hydrocarbons, particulate matter such as sand and grit, and miscellaneous debris such as vegetative matter, paper, plastic, and foam cups. For example, about 200 pounds of miscellaneous debris and 500 pounds of sand and grit is commonly carried off by storm-water runoff from some one-acre parking lots in 90 days.
To maintain freshwater systems, most cities and counties have regulations requiring that some of the pollutants be removed from the storm-water runoff before entering their storm sewer systems. In order to meet these regulations, facilities typically install on-site pollution traps to filter the storm-water runoff. These pollution traps are sometimes referred to as xe2x80x9coil/grit separators.xe2x80x9d
Most conventional pollution traps provide only xe2x80x9cfirst flushxe2x80x9d filtration during the typical local storm event, but permit bypassing the filtration stage for larger storms. In fact, many jurisdictions require bypassing, some even at typical storm water flows. Bypassing filtration is a problem because most pollutants are more easily picked up and transported by storm water during higher flow periods. Unfortunately, just when the traps are needed most, a lot of pollutants bypass them and are delivered into the storm sewer systems. And most pollution traps that do not provide for bypassing accommodate the larger flows because they are oversized, which adds significantly to the cost to build, install, and maintain them.
Another problem with many pollution traps is they simply filter the storm water at the natural flow rate of the storm water passing through it. The faster the storm water flows through the trap, the less particulate matter pollutants can settle in the trap. Some other traps detain the storm water for a brief time to allow some of the particulate matter to settle. But these traps only detain the water for a few minutes at most, and even a small water flow will cause the particles to be re-suspended in the water. Therefore, these pollution traps allow a lot of particulate matter pollutants to pass though them, even before bypass occurs.
In addition, the filtering systems of some pollution traps include screens for capturing miscellaneous debris. These screens are typically partially submerged in the water in the middle of the trap so that the debris is always floating in the water. Because the debris is always floating, it does not block the screen. The problem with this configuration is that vegetation, paper, and other absorbent miscellaneous debris tends to become waterlogged, rot, and deteriorate into smaller parts. These small parts then pass through the screen, are re-suspended in the water, and are carried out of the trap. Moreover, vegetative matter contains nitrogen and phosphorus and carries other pollutants such as fertilizer, pesticides, and oils. And paper products carry inks and other surface adherents. So now these additional pollutants also pass through the screen with the deteriorated debris and out of the trap.
Accordingly, it can be seen that a need remains for a pollution trap that stays on-line and filters all the storm-water runoff from a parcel of land, without bypassing filtration or overflowing during larger-than-typical storms. In addition, there is needed a pollution trap that better induces settling of particulate matter and reduces waterlogging of absorbent miscellaneous debris, to provide improved filtration of pollutants from the storm water. Furthermore, a need exists for such a pollution trap that is cost-efficient to build, install, and maintain. It is to the provision of a pollution trap meeting these and other needs that the present invention is primarily directed.
The present invention provides an innovative trap for separating pollutants from storm water runoff. The trap separates pollutants such as miscellaneous debris including vegetative matter, plastic, and paper, particulate matter including sand, grit, and clay, and/or floating matter including motor oil, other hydrocarbons, and detergents. In addition, the trap can be used to separate other pollutants from other liquids, as may be desired in a particular application.
Generally described, the pollution trap includes a chamber, a screen, one or more baffles, a collection reservoir with a skimming edge, and a pivotal filter. The chamber has an inlet, an outlet, a floor, a worst storm water level when the water is flowing through the chamber at a maximum water flow rate, and an at-rest water level when none of the water is flowing into the chamber. The screen, the baffles, the collection reservoir, and the pivotal filter are each positioned in the chamber between the inlet and the outlet.
The screen is configured to suspend at least some of the miscellaneous debris or other pollutants above the at-rest liquid level. The baffles are configured to increase water residence time in the chamber to encourage settling of the particulate matter or other pollutants. The collection reservoir is configured to skim at least some of the floating matter or other pollutants into it. And the pivotal filter is configured to filter out at least some of the clay or other pollutants.
In an exemplary embodiment of the present invention, the screen is positioned at or above the at-rest water level so that the screen retains some of the pollutants, allows the water to pass through it, and suspends the retained pollutants above the at-rest water level. In this way, the suspended retained pollutants are kept dry when there is no storm so that they do not waterlog, deteriorate, and pass through the screen. The screen can be, for example, basket-shaped but with an open side adjacent the inlet.
The baffles are each configured and positioned in the chamber to form at least one gap through which the water may flow around the baffle. In this way, the water flows around the baffles in a longer flow route through the chamber, without flowing any faster. Preferably, the collective flow area through the baffles is significantly greater than the flow area of the inlet to cause the linear speed of the flow to slow substantially while maintaining the volume of the flow constant. This increases the residence time of the water in the chamber, which encourages settling of some of the pollutants.
For example, two baffles can be provided with the first baffle having a bottom gap to encourage the water to flow over it and the second baffle having a top gap to encourage the water to flow under it. In this configuration, the water flows under the first baffle through the bottom gap and then back up and over the second baffle through the top gap. Of course, the baffles can be provided in other configurations such as with side gaps, intermediate gaps, corner gaps, or a combination of these.
In addition, the baffles may have apertures in them that permit at least some of the liquid to pass through them. In this way, the apertured baffles disperse the water, which further encourages settling of some of the pollutants.
The collection reservoir has a skimming edge that is positioned at or adjacent the worst storm water level to skim floating pollutant matter into the collection reservoir. As the water flow through the chamber increases during larger-than-typical storms, the floating pollutants rise with the water level until they are skimmed off the surface of the water and into the reservoir, instead of bypassing the trap. In order to provide for adjusting the skimming edge for the maximum water flow at a particular installation, the skimming edge may be provided on a weir member that is vertically adjustable and mounted to a front wall of the collection reservoir.
In addition, the bottom of the collection reservoir may be positioned above the chamber floor to permit the water to flow under the collection reservoir. In this way, the water flow route through the chamber is increased to further encourage settling of some of the pollutants.
The pivotal filter pivots from a filtering position when a typical flow of the water is flowing through it toward a bypass position in response to a larger-than-typical flow of the water pushing against it. In this way, the pivotal filter stays in the filtering position during typical storms or between storms. But during larger-than-typical storms, the force of the water against the pivotal filter pushes it out of the way so that it does not impede the flow of the water out of the chamber. The pivotal filter may include, for example, a fibrous filtration member made of coconut fiber or another material for filtering clay or other particulate matter.
Preferably, the screen is positioned adjacent the inlet, the baffles between the screen and the outlet, the collection reservoir between the baffles and the outlet, and the pivotal filter between the collection reservoir and the outlet. Also, the screen, the baffles, the collection reservoir, and the pivotal filter each preferably extend substantially all the way across the chamber so that the water does not flow around them. In some embodiments, however, the baffles have side gaps, intermediate gaps, corner gaps, or a combination of these, in which case they do not extend all the way across the chamber.
In this exemplary embodiment, the screen, baffle, reservoir, and pivotal filter filtration stages cooperate to provide a significant increase in performance over conventional pollution traps. In particular, the screen suspends at least some of the miscellaneous debris above the at-rest water level, the baffles increase water residence time in the chamber to encourage settling of the particulate matter, the collection reservoir skims at least some of the floating matter into it but allows the water to flow under it, and the pivotal filter filters out at least some of the suspended clay. It will be understood by those skilled in the art that these filtration stages can be used in this or other configurations for separating other pollutants from other liquids.
In addition, a method of the present invention provides steps for maintaining the pollution trap in good working condition. The method includes the steps of opening the chamber, removing the pollutants from the trap, and closing the chamber. The step of removing the pollutants from the trap includes removing the miscellaneous debris from the screen, suctioning the settled particulate matter from the chamber floor, suctioning the floating matter from the collection reservoir and/or the storage container, and removing the clay retained by the pivotal filter. The step of removing the miscellaneous debris from the screen can be carried out by removing, emptying, and replacing the screen. And before the step of suctioning the floating matter, the maintenance plug may be removed or the weir may be lowered to allow built-up floating matter to drain into the collection reservoir.
Accordingly, the pollution trap stays on-line and routes all the storm-water runoff through it, instead of bypassing or overflowing during larger-than-typical storms. In particular, the pollution trap collects floating hydrocarbons and particulate matter during larger-than-typical storms, when more of these pollutants are carried by the storm water. Additionally, the pollution trap reduces waterlogging of absorbent miscellaneous debris and better induces settling of particulate matter, thereby providing improved filtration of pollutants from the storm water. Furthermore, the pollution trap is cost-efficient to build, install, and maintain.
These and other features and advantages of the present invention will become more apparent upon reading the following description in conjunction with the accompanying drawing figures.